CO.sub.2 lasers are now being extensively used in medical, industrial and military applications, and a variety of optical fibers and hollow flexible waveguides have been proposed as the transmission medium for these applications. However, only hollow waveguides have proven to be economically and commercially possible for transmitting a relatively high flux of CO.sub.2 laser energy.
Although dielectric-coated hollow waveguides for transmitting electromagnetic waves have been studied since the 1950's, the fabrication method for dielectric-coated hollow flexible waveguides at infrared CO.sub.2 laser wavelengths was not reported until 1983. (M. Miyagi, et al., entitled "Fabrication of Germanium-coated Nickel Hollow Waveguides for Infrared Transmission", Appl. Phys. Lett., Vol. 43, No. 5, Sep. 1 1983.) Since then, various versions of that waveguide have been suggested and made by other groups.
Hollow waveguides are now used more often to transmit laser light in medical and industrial applications. In particular, the transmission of laser light at very different wavelengths (10.6 .mu.m and 0.6328 .mu.m) is ideally suited for hollow waveguides. Rigid hollow waveguides made of hollow alumina ceramic tubes encased in a stainless steel jacket have been used extensively to transmit a CO.sub.2 laser light in rigid endoscopic applications. (See U.S. Pat. No. 4,917,083, Apr. 17, 1990). These waveguides, however are limited in both length and power handling and can readily overheat or melt when the laser light is not properly launched into the waveguide. Also, ceramic tubes are not flexible due to their inherent lack of ductility, precluding their use in flexible waveguides.
Some types of known hollow metallic waveguides are not flexible enough and tend to overheat, limiting the maximum input power. Another plastic type of flexible hollow waveguide has a larger inside diameter and a lower power transmission efficiency.
The following United States patents disclose hollow waveguides and lightpipes for lasers: U.S. Pat. No. 4,652,083 to Laakmann on Mar. 24, 1987 for "Hollow Waveguide", U.S. Pat. No. 4,688,892 to Laakmann on Aug. 25, 1987 for "Hollow Waveguide Having Disparate Dielectric overcoating", U.S. Pat. No. 4,688,893 to Laakmann on Aug. 25, 1987 for "Hollow Waveguide Having Plural Layer Dielectric", U.S. Pat. No. 4,805,987 to Laakmann on Feb. 21, 1989 for "Hollow Waveguide Using A Low Refractive Index Inner Layer", U.S. Pat. No. 4,913,505 to Levy on Apr. 3, 1990, "Hollow Lightpipe and Method for Its Manufacture", U.S. Pat. No. 4,930,863 to Croitoriu et al. on Jun. 5, 1990 for "Hollow Fiber Waveguide And Method of Making Same", and U.S. Pat. No. 4,917,083 to Harrington et al. on Apr. 17, 1990 for "Delivery Arrangement for A Laser Medical System". These patents are hereby incorporated by reference.